EFFECT OF CAFFEINE ON SUBMAXIMAL EXERCISE PERFORMANCE AT ALTITUDE

The purpose of this study was to determine if caffeine (CAF) could enh ance exercise performance at high altitude (HA). Eight males (17 to 24 years) performed two submaximal endurance tests to exhaustion (ETX) w hile cycling at approximately 80% of their altitude-specific maximal a erobic power during each of three phases: 1) sea level (SL); 2) after 1 h (acute) at 4,300 m; and 3) after 2 weeks (chronic) at 4,300 m. Sub jects received either CAF (4 mg . kg-1) or a placebo drink 1 h prior t o each ETX bout at each phase in a double-blind crossover design. ETX was little affected during CAF treatment at SL (26.33 to 27.51 min, p = 0.21) but was increased by 54% (22.77 to 35.10 min, p = 0.004) durin g acute HA exposure and tended to improve (24%, 30.52 to 38.63 min, p = 0.084) during chronic HA exposure. The change in ETX during acute AL T could not be accounted for by differences in substrate metabolism, Q , diet, or RPE, but may have been due to either a CAF-induced increase in tidal volume or to a lessening of an ALT-induced impairment in mus cular force production during submaximal exercise.